In line with the increasing capacity of magnetic recording media, the data transfer speed in VTRs and computer drives has been increased by raising the relative running speed of a magnetic recording medium with respect to a magnetic head. Improvement on recording density is indispensable for achieving high capacity, and magnetic recording media with excellent electromagnetic characteristics have been demanded.
Very fine and highly coercive ferromagnetic metal powder and hexagonal ferrite powder have been used in pursuit for improved recording density.
Further increased recording density has been sought by reducing the thickness of a magnetic layer formed of such fine, high-coercivity ferromagnetic powder thereby minimizing read output reduction caused by thickness loss. For example, JP-A-5-182178 discloses a magnetic recording medium having a substrate, a non-magnetic lower layer containing inorganic powder dispersed in a binder, and a magnetic upper layer having a thickness of 1.0 μm or smaller and containing ferromagnetic powder dispersed in a binder, the magnetic upper layer having been formed while the non-magnetic lower layer is wet. These technologies have introduced various magnetic recording tapes with such a dual layer structure, including those for computers such as DLT IV, DDS3, DDS4, LTO, SDLT, and DTF2 formats, and those for broadcast such as a DVC pro format.
Approaches to high capacity and high density magnetic recording media include developing novel fine magnetic powder, optimizing the dual layer structure, optimizing magnetic characteristics, and smoothing the magnetic layer surface. From the aspect of magnetic recording derives, studies on shortening of recording wavelength for increasing recording density have been conducted with the focus on a magnetic recording head. An inductive magnetic head for reproduction relying on electromagnetic induction should have an increased number of coil turns in order to obtain an increased read output. However, this causes an increase in inductance and an increase in resistance in the high frequency region, which eventually results in reduction of read output. Therefore, there is a limit in reachable recording density with an inductive magnetic head.
On the other hand, a head for reading based on magnetoresistive effects, i.e., a magnetoresistive (MR) head has now come to be used on hard disks, etc. An MR head provides a few times as much output as an inductive head. Having no inductive coil, an MR head achieves great reduction of noise created by equipment, such as impedance noise, to bring about improvement on high density recording and reproduction characteristics. Therefore, an MR head, being promising for improvement on high-density recording reproduction, has been steadily extending its application in computer drives including linear tape-open (LTO) drives.
In an attempt to bring out the potential of a drive equipped with an MR head, the inventors of the present invention have hitherto studied smoothing the surface of a magnetic layer by, for example, designing a proper magnetic layer formulation or developing a smooth substrate or optimizing calendering conditions. However, when a magnetic recording tape with a backcoating layer is stored or handled for processing in form of a tape pack (roll) wound on a hub, the surface roughness profile of the backcoating layer can imprint itself in the magnetic layer under compressive force exerted in the normal directions of the roll. Such an imprint has now turned out to cause deterioration in S/N characteristics or increased error rates. To overcome the roughness imprint problem, it has been attempted to smoothen the backcoating layer surface, but back side smoothening results in increased friction and poor tape pack wind quality in a running test.